There are two main types of yeast you will find on the grocery store shelves: active dry yeast and instant yeast.

Active dry yeast has larger grains and needs to be “proofed” (dissolved in water) before using. The point of proofing is simply to hydrate or dissolve the yeast before adding it to the dough. In the past, the proofing stage was also used to determine if the yeast was still active or not, and involved the addition of a small amount of sugar, but with modern production this is largely unnecessary.

Instant yeast is often labeled as quick rise yeast because it is more concentrated than active dry yeast. Instant yeast has much smaller grains than active dry and does not need to be proofed or hydrated before using. Instant can be added directly to the flour before mixing.

Converting:

1 tsp Active Dry = 2/3 tsp Instant (100% Active Dry = 66% Instant)

1 tsp Instant = 1 1/2 tsp Active Dry (100% Instant = 150% Active Dry)

You can substitute one for the other in any recipe. Remember that active dry must be dissolved in a small amount of lukewarm water before you use it.